This research focuses on desiccation cracking, and on the need to develop geometric information on crack geometry through the development of nondestructive testing techniques or application to fine grained soils that are susceptible to changes in properties including strength, volumetric relationships, and hydraulic properties. The objective of the proposed research is to develop an ultrasonic nondestructive testing technique to determine the depth of desiccation cracks in clay soils and to relate the depth of cracking to various clay properties. The investigators will formulate a series of predictive equations relating to the development and propagation of cracks, such as: depth of cracking, surface crack density, and rate of crack propagation as a function of plasticity and activity, mineralogy, initial water content, compaction conditions, and strength of soils, and wetting and drying cycles applied to the soils. The crack characteristics that will be analyzed experimentally include soil moisture suction corresponding to crack initiation, depth of propagation, surficial geometry, rate of crack propagation, and moisture flux through cracks, with a focus on the effects of cracking on hydraulic properties of the soils. The research will experimentally determine the modification of flow through the clay as a result of the presence of cracks. The ultrasonic method will provide an innovative tool to analyze the depth of cracking in soils, and will be used together with previously developed image analysis techniques to determine 3-D characteristics of cracks. These two methods can be applied to analyze tension cracks, freeze/thaw cracks, or any other type of crack developing in soils. The ultrasonic equipment can also be readily transported to the field for tests, and photographs of the desiccation process are the only input required for the image analysis. The predictive equations will allow for determining extent of cracking using basic soil characterization data as opposed to complicated theoretical solutions. Results of the research will apply to design and construction of engineering structures on soils susceptible to cracking and construction of waste containment facilities. In addition, the results will apply to groundwater recharge problems, contaminant transport in the vadose zone, and agricultural problems.
